Luminance/chrominance separator

Abstract

When separating a composite video signal into a luminance signal component and the chrominance signal component by the use of filtering, a high frequency cross-talk component of the luminance signal is present in the chrominance signal and this may be cancelled using a horizontal correlator that imparts time delays and detects maximum and minimum levels relative to a reference level. In such luminance cross-talk cancellation by means of the horizontal correlator the usable chrominance signal length is shortened by almost one wave length out of four, thereby reducing the usable chrominance signal each time such luminance/chrominance signal separation occurs in a dubbing operation, for example. By utilizing two chroma separators in series each including a nonadditive mixer circuit, the resultant output from the second chroma separator circuit has substantially the same length as the portion of the composite video signal fed as the input. As a further safety factor in preventing the chrominance signal from being produced with excessive noise, a time delayed version of the composite video signal is level checked with the output of the second chroma separator unit and the signal having the lesser level is produced as the output.

What is claimed is: 
     
       1. Apparatus for removing high-frequency luminance cross-talk components from a chrominance signal modulated on a chrominance subcarrier signal and formed as part of a composite video signal of specified length, comprising: first chroma separator means receiving said composite video signal and including first delay means for imparting a first time delay based on a period of said chrominance subcarrier signal to said composite video signal and producing a first time delayed output and first signal synthesizer means receiving said composite video signal and said first time delayed output for producing therefrom a first horizontally correlated, synthesized output signal formed of said chrominance signal and reduced cross-talk components; and   second chroma separator means receiving said first horizontally correlated, synthesized output signal from said first chroma separator means and including second delay means for imparting to said synthesized output signal a time delay corresponding to said first time delay and producing a second time delayed output therefrom and a second signal synthesizer means receiving said second time delayed output and said first horizontally correlated, synthesized output signal from said first chroma separator means for producing therefrom a second horizontally correlated, synthesized output signal having a length substantially equal to said specified length of said composite video signal.   
     
     
       2. Apparatus according to claim 1, in which said first delay means includes a first delay line having a time delay equal to the period of 1/2 the wavelength of said chrominance subcarrier signal. 
     
     
       3. Apparatus according to claim 2, further comprising a signal inverter for inverting said first time delayed signal and said inverted first time delayed signal being fed to said first synthesizer means. 
     
     
       4. Apparatus according to claim 3, in which said first delay means further includes a second delay line having a time delay equal to the period of 1/2 the wavelength of said chrominance subcarrier signal and receiving said first time delayed signal from said first delay line and the output of said second delay line being fed to said first synthesizer means. 
     
     
       5. Apparatus according to claim 1, in which said second delay means includes a first delay line having a time delay equal to the period of 1/2 wavelength of said chrominance subcarrier signal. 
     
     
       6. Apparatus according to claim 5, further comprising a signal inverter for inverting said second time delayed signal and said inverted second time delayed signal being fed to said second synthesizer means. 
     
     
       7. Apparatus according to claim 6, in which said second time delay means further comprises a second delay line having a time delay equal to the period of 1/2 the wavelength of said chrominance subcarrier signal and receiving said second time delayed signal from said first delay line of said second delay means and producing an output therefrom fed to said second synthesizer means. 
     
     
       8. Apparatus according to claim 1, further comprising selector circuit means receiving said first time delayed output and said second horizontally correlated, synthesized output signal from said second synthesizer means for selecting therebetween the signal having the lowest relative level. 
     
     
       9. Apparatus according to claim 8, in which said selector circuit means includes: first maximum detecting circuit receiving said first time delayed output and a reference level signal for reproducing the signal having the greater level as an output signal;   second maximum detecting circuit receiving said output signal from said second signal synthesizer means and said reference level signal for reproducing the signal having the greater level as an output signal;   first minimum detector circuit receiving said output signals from first and second maximum detecting circuits for reproducing the signal having the lesser level as an output signal;   second minimum detecting circuit receiving said first time delayed output and said reference level signal for reproducing the signal having the lesser level as an output signal;   third minimum detecting circuit receiving said output signal from said second signal synthesizer means and said reference level signal for reproducing the signal having the lesser level as an output signal;   third maximum detecting circuit receiving said output signals from said second and third minimum detecting circuits for reproducing the signal having the greater level as an output signal; and   mixer means receiving said output signals from said first minimum detecting circuit and said third maximum detecting circuit for producing a nonadditive mixed output signal therefrom.   
     
     
       10. Apparatus according to claim 1, in which said second signal synthesizer means includes maximum detecting means receiving said output from said first signal synthesizer means, said second time delayed output and a reference level signal for reproducing the signal having the highest positive level as an output signal; minimum detecting means receiving said output signal from said first signal synthesizer means, said second time delayed output, and said reference level signal for reproducing the signal having the lowest negative level as an output signal;   and mixer means receiving said output signals from said maximum detecting means and said minimum detecting means for producing a nonadded mixed output signal therefrom.   
     
     
       11. Apparatus according to claim 10, in which said maximum detecting means includes a plurality of maximum level detecting circuits each receiving at one input said reference level signal and at another input one of said first time delayed output or said composite video signal and each reproducing as an output signal the signal having the greater level, and a further maximum level detecting circuit receiving said output signals from said plurality of maximum level detecting circuits for reproducing as an output signal the signal having the highest level. 
     
     
       12. Apparatus according to claim 10, in which said minimum detecting means includes a plurality of minimum level detecting circuits each receiving at one input said reference level signal and at another input one of said first time delayed output or said composite video signal and each reproducing as an output signal the signal having the lowest level, and a further minimum level detecting circuit receiving said output signals from said plurality of minimum level detecting circuits for reproducing as an output signal the signal having the greatest level. 
     
     
       13. Apparatus according to claim 1, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a bandpass filter receiving said composite video signal for filtering therefrom substantially all of said luminance signal and producing a filtered output signal fed as said composite video signal to said first chroma separator means. 
     
     
       14. Apparatus according to claim 1, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a bandpass filter means receiving said second horizontally correlated, synthesized output signal from said second synthesizer means for filtering therefrom substantially all of said luminance signal. 
     
     
       15. Apparatus according to claim 1, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a selector circuit connected to receive said first time delayed output and said second horizontally correlated, synthesized output signal from said second synthesizer means for producing an output signal corresponding to the input signal having a lower level, and bandpass filter means receiving said output signal from said selector circuit for filtering therefrom substantially all of said luminance signal. 
     
     
       16. A circuit for removing high-frequency cross-talk from a chrominance signal modulated on a chrominance subcarrier signal and formed as a portion of a composite video signal having predetermined time length, comprising: a first chroma separator receiving said composite signal and including first delay means for providing a first time delay based on a period of said chrominance subcarrier signal and producing a corresponding first delayed output, and a first signal synthesizer receiving said portion of said composite video signal and said first delayed output for producing therefrom a horizontally correlated, synthesized output signal formed of said chrominance signal with reduced cross-talk and having length less then said predetermined time length; and   second chroma separator means receiving said horizontally correlated, synthesized output signal from said first chroma separator means and including second delay means for providing a time delay corresponding to said first time delay and producing a second delayed output, and a second signal synthesizer receiving said second delayed output and said horizontally correlated, synthesized output signal from said first chroma separator means for producing therefrom a second horizontally correlated, synthesized output signal having a length substantially equal to said predetermined time length of said composite video signal.   
     
     
       17. A circuit according to claim 16, further comprising selector circuit means receiving said first delayed output and said second horizontally correlated, synthesized signal from said second signal synthesizer for reproducing the signal having the lowest relative level as an output signal. 
     
     
       18. A circuit according to claim 17, in which said selector circuit means includes: first maximum detecting circuit receiving said first delay output and a reference level signal for reproducing the signal having the greater level as an output signal;   second maximum detecting circuit receiving said output signal from said second signal synthesizer and said reference level signal for reproducing the signal having the greater level as an output signal;   first minimum detector circuit receiving said output signals from first and second maximum detecting circuits for the signal having the lesser level as an output signal;   second minimum detecting circuit receiving said first delayed output signal and said reference level signal for reproducing the signal having the lesser level as an output signal;   third minimum detecting circuit receiving said output signal from said second signal synthesizer and said reference level signal for reproducing the signal with the lesser level as an output signal;   third maximum detecting circuit receiving said output from said second and third minimum detecting circuits for reproducing the signal having the greater level as an output signal; and   mixer means receiving said output signals from first minimum detecting circuit and said third maximum detecting circuit for producing a nonadditive mixed output signal therefrom.   
     
     
       19. Apparatus according to claim 16, in which said second synthesizer means includes maximum detecting means receiving said output signal from said first signal synthesizer means, said second delayed output, said and a reference level signal for reproducing the signal to the highest level as an output signal; minimum detecting means receiving said first delayed output, said composite video signal, and said reference level signal for reproducing signal having the lowest level as an output signal;   and mixer means receiving said output signal from said maximum detecting means and said minimum detecting means for producing a nonadditive mixed output signal therefrom.   
     
     
       20. Apparatus according to claim 19, in which said maximum detecting means includes a plurality of maximum level detecting circuits each receiving at one input said reference level signal and at another input one of said second delayed output or said output signal from said first signal synthesizer and each reproducing as an output signal means, the signal having the greater level, and a further maximum level detecting circuit receiving said output signals from said plurality of maximum level detecting circuits for reproducing as an output signal the signal having the highest level. 
     
     
       21. Apparatus according to claim 19, in which said minimum detecting means includes a plurality of minimum level detecting circuits each receiving at one input said reference level signal and at another input one of said second delayed output or said output signal from said first signal synthesizer means, and each reproducing as an output signal the signal having the lowest level, and a further minimum level detecting circuit receiving said output signals from said plurality of minimum level detecting circuits for reproducing as an output signal the signal having the lowest level. 
     
     
       22. Apparatus according to claim 16, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a bandpass filter receiving said composite video signal for filtering therefrom substantially all of said luminance signal and producing a filtered output signal fed as said composite video signal to said first chroma separator means. 
     
     
       23. Apparatus according to claim 16, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a bandpass filter means receiving said second horizontally correlated, synthesized output signal from said second synthesizer means for filtering therefrom substantially all of said luminance signal. 
     
     
       24. Apparatus according to claim 16, in which said composite video signal is formed of a luminance signal component and said chrominance signal and further comprising a selector circuit connected to receive said first time delayed output and said second horizontally correlated, synthesized output signal from said second synthesizer means for producing an output signal corresponding to the input signal having a lower level, and bandpass filter means receiving said output signal from said selector circuit for filtering therefrom substantially all of said luminance signal.